We might speak about new portage features to handle dependencies, preserved libs... or even its crappy speed because of all those features added to ease the life of gentoo today.

But i don't get your rant about something that was happening 10 years ago already like if it wasn't.

Well, i remember 10 years ago, i used ~x86, today i'm still, but 10 years ago, ~ was really unstable and i have to fix many things on my own or mask them.
Today, devs keep masking problematic packages, and the ~ branch name doesn't fit it anymore, nor it fulfil its need, 10 years ago, i try to install a package, it doesn't even compile, bugreport, fix in the bugreport, add the fix, test, report working or not, and package was fixed...
Today devs looks alone with their mask set, and it's hard to find a package that doesn't even compile anymore from ~
From users point of view it's better, from dev or package stabilization it's worst, because increasing quality of ~ in my opinion has ease ~ users life at the cost of decreasing stable users (not for its stability, but because ~ aren't test users anymore, package can takes a long time now to be stabilize).

It could also be an issue in the dependency resolver of portage. (Perhaps not algorithmitcally, but maybe some new subslots dependency causes some loop which must be broken somewhere and such leads to incorrect results).
In fact, if slim DEPENDs on cmake then cmake should have been updated to current stable before slim is emerged, so this issue should not arise.
Similarly, if chromium depends directly or indirectly on perl then perl should have been updated before chromium is compiled. (That perl-updater must possibly be run in between is clear and was always the case.)
So I suggest if it really happens for you that a package is updated before a dependency is updated that you report a bug.

Edit: I assume here that you use something like

Code:

emerge -NaDu --with-bdeps=y @world

to update your machine; otherwise, it is a usage error, and you cannot blame gentoo for that